066 with 385xp piston

[XP_Slinger]

Holy *s-worde that Saw sounds strong Jim. Outstanding work as usual.

 

[Chainsaw Jim]

Well, I've been busy on other saws and haven't had time to upload any pics of my progress. A belated big thank you to @jacob j. for the crankshaft.

 

[Chainsaw Jim]

I went a little crazy on the piston, lol. It didn't kill the compression though, it still pumps up to 200. The brand new ring still needs beak in time so it has potential to climb a little higher.


I did a better job this time installing the 1128 series coil. The first time I used the 064 case I made it a little ugly on the coil fitment...



This time I swapped out the armature with the 064 coil for a direct fit.

 

[drf256]

What’s with the piston Jim? Pressure holes to push the ring to the bore?

Does the crown have an angle to it, or is that an illusion?

 

[Sty57]

What’s with the piston Jim? Pressure holes to push the ring to the bore?

Does the crown have an angle to it, or is that an illusion?

Sure looks like gas porting to me.

 

[jacob j.]

Sure looks like gas porting to me.

I have an .050" over Mac 101b piston with similar holes and the old timers told me they did that to keep the cylinder pressure up at high RPM.

 

[Chainsaw Jim]

What’s with the piston Jim? Pressure holes to push the ring to the bore?

Does the crown have an angle to it, or is that an illusion?

Yes, and the crown does have a slight pop up. I couldn't take any more material from the cylinder to get the squish set at .020".

I also had to mill the skirt O.D. down by .003" for better clearance. It started out at .001" and was slowing things down.

 

[Sty57]

I have an .050" over Mac 101b piston with similar holes and the old timers told me they did that to keep the cylinder pressure up at high RPM.

I've never seen one of them Big Mac's.
But I'm guessing they ran thin rings in them.
I could see gas porting might help them seal up and with ring flutter at high RPM.

Downside is they'll wear out faster and add to the maintenance of the engine. As the hole need to be kept clean from carbon.

I like the idea and it's one of them things. That youll never know until you try it.

 

[Sty57]

I wonder if a lateral gas port would be a little better with sealing. When the transfers crack open.

 

[srcarr52]

Vertical gas ports gain pressure faster than lateral. Lateral are better for really high flame front temps where you don't want an exposed corner.
We had to vertical gas port alcohol kart (gx200) engines or they wouldn't never seat the rings and burn oil all the time.

 

[Chainsaw Jim]

Here's a few cuts after a little port work. The ring is brand new and needs a few heat cycles. Still running stock intake system, including filter.

 

[RI Chevy]

Sounds real good Jim. Nice job.

 

[661joe]

Found it lol

 

[661joe]

Runs good

 

[Chainsaw Jim]

I found a nice little filter for improvisational use on the old style tank vents. It's a Zama brand fuel filter and I have no idea what it's for. I asked the parts guy at the stihl shop for the smallest filter they had available and that's what he came out with.

 

[661joe]

I like the filter lol for some reason it's much more appeling.

 

[Chainsaw Jim]

One more round on the bench for a carb mod. It seems to have picked up a little bit from it.

 

[661joe]

Good running saw. Can really lean on it

 

[Frank bierce]

Very nice Jim!

 

[blsnelling]

One more round on the bench for a carb mod. It seems to have picked up a little bit from it.

Sounds great.